Chemical and Physical Absorption of SO₂ by N-Functionalized Imidazoles: Experimental Results and Molecular-level Insight

Abstract

Sulfur dioxide (SO 2 ) removal is a key component of many industrial processes, especially coal-fired power generation. Controlling SO 2 emissions is vital to maintaining environmental quality, as SO 2 is a contributor to acid rain, but has value as a chemical feedstock. Although a number of novel solvents/materials including ionic liquids (ILs) have recently been proposed for alternatives to limestone scrubbing for SO 2 capture/removal from point sources, the imidazole architecture presents a convenient, inexpensive and efficient class of low volatility and low viscosity solvents to accomplish this goal. On the basis of our prior work with imidazoles for CO 2 capture, we have extended our interests toward understanding the relationship between imidazole structure and SO 2 absorption. Using a series of imidazole compounds with various substituents at the 1, 2 and/or 4(5) positions of the five-membered ring, SO 2 absorption via both chemical and physical mechanisms was observed. The chemical absorption product is a relatively stable 1:1 SO 2 −imidazole complex, while physical absorption of SO 2 is dependent on pressure and temperature. Because imidazoles are relatively small molecules, they are an efficient absorption medium for SO 2 and can form adducts wherein the mass fraction of bound SO 2 is >40 wt %. The SO 2 −imidazole complexes were also observed to produce distinct color and/or phase changes that are associated with the nature of the substituents present. The chemically bound SO 2 can be released under vacuum at moderate temperature (∼100°C) and vacuum, yielding the original neat solvent, while the physically dissolved SO 2 can be readily removed at ambient temperature under vacuum. This behavior corresponds to a much smaller enthalpy of absorption for physical dissolution (−4 to −13 kJ/mol) as determined via thermodynamic relationships compared to the binding energies of chemical complexation (−35 to −42 kJ/mol) as determined via density functional theory calculations. Increasing chemical complexation energies are correlated with increased substitution on the imidazole ring. Simulations were also employed to gain insight into the structures of the SO 2 −imidazole complexes, illustrating changes in partial charge distribution before and after complexation as well as confirming a charge transfer complex is formed based on the N−S bond length.

Absorption, desorption and spectroscopic investigation of sulfur dioxide in the binary system ethylene glycol+dimethyl sulfoxide

“…The characteristic peak at 3376 cm À1 was assigned to stretching vibrational band of hydroxyl in EG [26], which was shifted to lowfrequency band from (3376 to 3361) cm À1 with the increasing content of DMSO in the binary system EG (1) + DMSO (2). This meaning that the addition of DMSO destroyed original hydrogen bonding of self-association among EG molecules firstly, and then the new hydrogen bonds were formed by cross-association between EG and DMSO.…”

“…SO 2 , which mainly emitted from fossil fuel burning power plants, sulfide-based metal smelters, petroleum, and other SO 2 -emitting industries, caused harmful impacts on the environment and human health [1][2][3]. Consequently, the control of the concentration level of SO 2 had been a worldwide issue to be urgently solved in the atmosphere [4][5][6].…”

“…To overcome disadvantages, EG was added into DMSO to drop the freezing point of DMSO and stabilize SO 2 absorption performance in the binary system EG (1) + DMSO (2). As a whole, the treatment of SO 2 by the binary system EG (1) + DMSO (2) included the following four steps: (1) density, viscosity, and excess properties for the binary system EG + DMSO, (2) absorption and desorption properties of SO 2 in the binary system EG + DMSO, (3) intermolecular interaction in the system EG (1) + DMSO (2) + SO 2 (3), and (4) simulation of industrial experiment. The first part was reported in the previous work [18], and the parts of (2) and (3) were researched in this work.…”

Polyoxometalate (POM)-Layered Double Hydroxides (LDH) Composite Materials: Design and Catalytic Applications

“…Also recently, we developed an intercalated hybrid material Mg3Al-IL-EuW10 that incorporates covalently anchored ionic liquids, and exhibits efficient deep desulfurization and high selectivity for the removal of 4,6-DMDBT and DBT etc. In addition to sulfur compounds, diesel oil, gasoline and jet fuel contain many nitrogen-containing compounds [49]; the combustion of these substances will release large amounts of nitrogen oxides, leading to the formation of acid rain with serious environmental consequences [50]. Although the concentration of nitrogen-containing compounds in fuel oils is relatively low, the competition with sulfur-containing components for the active sites of the catalysts [51,52], can lead to the inhibition of the deep desulfurization process.…”

Efficient concurrent removal of sulfur and nitrogen contents from complex oil mixtures by using polyoxometalate-based composite materials

“…acid rain etc.). 4,5 Thus, it is absolutely essential to develop economically viable solutions for the removal of sulfur and nitrogen content from chemical mixtures. Currently, the hydro-desulfurization (HDS) and hydro-denitrogenation (HDN) industrial solutions are mainly based on the utilization of Co−Mo or Ni−Mo catalysts operating at high temperature and pressure regimes in the presence of hydrogen atmosphere.…”